This invention relates to an apparatus for supplying water for use in a building and particularly to an apparatus which extracts from the water radon by a degasifying technique.
All mineral materials contain uranium in greater or lesser amounts. This uranium decays through a chain of other isotopes to produce radon-222, which has a half-life of 3.8 days. Radon is a gas which can get into indoor air through several paths. When radon decays, it produces a chain of short-lived daughters which can become bound to the walls of the lungs. When they decay, the radiation damages lung tissue and it is a significant cause of lung cancer. It is estimated that approximately 1,000 Canadians are killed each year by lung cancer resulting from the radioactive decay of radon daughters.
One significant path for radon to reach indoor air is through well water. Radon gas is dissolved into this water underground, due to the high solubility of gases in cold water. This water is then pumped into the pressurized household water system, then heated in a hot water tank. The randon does not come out of solution, in spite of the increase in temperature and the corresponding decrease in solubility, because of the pressure. However, when the hot water is throttled through a tap into the house, the radon is released into the household air. This is particular problem in showers and baths, where large volumes of water are used, but it also occurs in dish and clothes washing.
Municipal water systems which draw their water from rivers and streams are relatively free of radon. Well water systems, whether municipal or private often contain significant amounts of dissolved radon. Attention has been given therefore to the removal of radon from the water supply system of a building.
For example U.S. Pat. No. 4,371,383 (Rost issued Feb. 1, 1983) discloses a tank which is placed additionally into the water supply line of a building in which the water entering the building is sprayed in a fine mist onto a number of separation plates. This arrangement has not met with significant commercial success in view of the fact that the technique does not result in a high removal of the radon and in view of the fact that the equipment required is an addition to the conventional water supply system and accordingly constitutes an additional expense which many people will not bear for a problem which is not itself readily apparent.
East German Patent Application No. 218278 published Feb. 6, 1985 by Glaeser et al discloses an arrangement in which vapour issued on the reduction of pressure from hot water sprayed by nozzles inside a storage tank is partly condensed by make up water descending a trickle-tower mounted upwardly of and connected to the tank. The arrangement therefor uses again a spray technique and the device is intended as an additional piece of equipment in the building supply system. Furthermore the device is apparently intended as a large scale device for a district heating system as opposed to a water supply apparatus for a domestic or like building.
German Patent Application No. 3012590 discloses a hot water tank arrangement including a heating element, a cold water inlet at the base of the tank and, at the top of the tank, a hot water outlet and a gas outlet. The hot water outlet includes a gas trap which prevents gas escape. The gas outlet includes a control valve which prevents liquid escape but allows the gas to freely exit to atmosphere. The water within the tank is however maintained at operating pressure of the order of 40 p.s.i. and this will prevent or seriously inhibit the escape of gas and particularly radon from the tank. The arrangement therefore has not been effective and has not achieved commercial success.
It is one object of the present invention, therefore, to provide an improved water supply system which enable the extraction of radon gas from the water supply while using the requirement for heated water in the building to provide the energy of the gasification.
According to the invention, therefore, there is provided an apparatus for supplying water for use in a building comprising a substantially closed tank, a water inlet line into the tank, level sensing means for determining the level of water in the tank, valve means in said inlet line actuated by said level sensing means for maintaining the level above a predetermined minimum and below a predetermined maximum, heating means in the tank for heating the water, thermostat means for controlling said heating means so as to retain the temperature of the water below a boiling temperature, and vent means communicating with the tank above the maximum level and arranged to communicate with the atmosphere exteriorally of the building so as to release gases in the tank above said water level to atmosphere and so as to maintain pressure in said tank at atmospheric pressure.
Preferably the thermostat is arranged such that the water in the tank is heated to a temperature greater than the desired temperature of the heated water and there is provided a heat exchanger downstream from and separate from the tank for cooling the heated water with the water supply down to the required temperature.
In a further preferred arrangement, there is provided a larger heat exchanger in which the heated outlet water is cooled firstly to a desired temperature for heated water and secondly to a desired temperature for cool supply water. A heat pump may be used to further cool the cool water supply from the outlet water.